The present invention relates to AC power adapters, particularly AC power adapters for use with consumer electronics. More particularly, the present invention relates to an AC power adapter with a multiple DC output.
Many different electronic devices are powered by direct-current (DC) voltage, as well as alternating-current (AC) voltage. However, standard line voltage available from wall outlets is AC. Therefore, the AC voltage must be convened to a DC voltage by an AC adapter to be used in these electronic devices.
AC adapters convert AC voltage (for example, 110 volts at 60 Hertz) from a standard wall outlet to a DC voltage (for example, 12 volts) which is useable by an electronic device such as a calculator, portable stereo, video game, and so on.
AC adapters generally include a plug which plugs into a wall outlet, a transformer which steps the line voltage down, a rectifier circuit which rectifies the stepped-down AC voltage to a DC voltage, and a plug which plugs into an electronic device. Numerous types of adapters have been developed, each having a rated voltage for a particular device and each having a plug which has a particular configuration engageable with a compatible socket of that particular device. Accordingly, separate AC adapters are typically provided for each electronic device.
Many times, however, certain electronic devices require more than one DC voltage input for operation of all the components of the device. As a result, AC power adapters which provide multiple DC outputs (i.e., DC outputs at two or more voltage levels) have been developed.
FIG. 1 shows a typical multiple output power adapter 50. The power adapter 50 includes an AC input receptacle 52 which plugs into an AC power socket. The AC input receptacle 52 is connected to an input of a multi-output power converter circuit, such as that shown in FIG. 2. This multi-output power converter circuit converts the input AC voltage into multiple output DC voltages which are output from respective output terminals for each output DC voltage. The multi-output power converter circuit is contained within a housing 54, and the AC input receptacle 52 projects from the housing 54 such that it can be easily connected to a wall socket. The output terminals of the multiple output DC voltages are then connected to respective prongs of an electrical device connector 56 via output wires 58.
Because of this multiple output power adapter design, the housing portion 54 of the adapter 50 which plugs into an AC power socket and contains the multi-output power converter circuit is relatively large. Further, since all of the components are located in the same housing, relatively long output wires 58 are required to be run from the circuitry within the housing 54 to the prongs of the electrical device connector 56. Because relatively long wires 58 are used, this power adapter 50 consumes a relatively large amount of power and has a higher voltage drop from the housing 54 to the device connector 56, thereby decreasing the efficiency of the power adapter 50. Moreover, due to the complex design of the multi-output power converter circuit, the circuit occupies a large volume, has a large power consumption, low efficiency, poor output regulation, and a high manufacturing cost.
Accordingly, there remains a need for a multiple output power adapter which is simple in design, inexpensive to manufacture and is highly efficient.